It's Susan Sarandon's 58th birthday and she's under press arrest in a Manhattan hotel suite conducting interviews for Alfie, the remake of the Sixties classic, in which Jude Law replaces Michael Caine as the adorable rogue. Ever the professional, Sarandon doesn't seem to mind that she's working on her birthday. "When you're in this business, you become very flexible in terms of holidays and birthdays. You sometimes have to move Christmas a week earlier or a week late," she smiles.

It's Susan Sarandon's 58th birthday and she's under press arrest in a Manhattan hotel suite conducting interviews for Alfie, the remake of the Sixties classic, in which Jude Law replaces Michael Caine as the adorable rogue. Ever the professional, Sarandon doesn't seem to mind that she's working on her birthday. "When you're in this business, you become very flexible in terms of holidays and birthdays. You sometimes have to move Christmas a week earlier or a week late," she smiles.

"My sons have already taken me out for my birthday dinner, and Tim [Robbins - her partner of 16 years] is playing with his band on the John Kerry tour registering people to vote. He's already given me a lovely gift of a beautiful hydrangea tree, which is planted outside our bedroom window, and, besides, he'll be singing down the phone in a few hours."

Sarandon is wearing grey tailored trousers and a multi-coloured short-sleeved blouse. Looking at least a decade younger, it's almost impossible to believe she will be collecting her pension in a few years. She is one of those women you wish to emulate in your later years (speaking as a woman). She is truly inspirational. A political campaigner, movie star, a longtime companion of a hot younger man, and a late-in-life mother. And, refreshingly, she takes herself less seriously than one might expect.

Her significant other is actor/director Tim Robbins (12 years her junior), whom she met when he was a fledgling actor on the set of Bull Durham (in which she starred opposite Kevin Costner) in 1988. He is the father of two of her three children, Jack Henry, 15, and Miles, 12. Her daughter, Eva, 19, is from her relationship with Italian director Franco Amurri. Robbins directed Sarandon in Dead Man Walking (1996), in which she played a nun consoling a death-row inmate (Sean Penn), and for which she collected a Best Actress Oscar. The death penalty is an issue close to her heart, and she still remains active in trying to overturn the legislation in various states.

"Of course it'd be amazing if more people got up in arms about it, but this is a country which gets more upset about a blow job than about hunger or education," she says. Sarandon is renowned for her provocative views on a myriad of subjects ranging from Aids, human rights, environmental issues and the plight of the Haitian refugees, a topic about which she was very vocal at the 1993 Academy Awards, to the dismay of some viewers.

She was involved in Vietnam protests and civil rights marches while a student at the Catholic University in Washington DC. Coincidentally, it was politics that first paved the career path of the New Jersey native. A couple of years after the 1968 Democratic convention, she attended an open casting call for the film Joe with her then husband Chris Sarandon (they divorced in 1979). Producers were searching for like-minded people who had disrupted the convention. Although she nailed the part, it was Chris, and not Susan, whose ambitions lay in acting.

"I like to say I'm here because all of my plans failed!" she laughs, glancing out the window at the view of people walking their dogs in Central Park. "I never wanted to be an actor. I never studied. Nothing. I just wanted to get out of New Jersey, so I went to college.

"I fell into everything. I think that is one of my strongest virtues which has served me the best. When something crossed my path, I was flexible enough to say: 'That looks interesting, let's give it a whirl'.

"That's true in my work too. You go in with a certain idea about what you don't want a character to be, but then you get a lot from the other actor and then suddenly you start to work with some kind of prop, and you discover that it's pretty funny. You make suggestions and maybe two end up taking you to a third thing, and that's the way I like to work."

Five years later, Sarandon starred in the most unlikely campy musical hit, The Rocky Horror Picture Show, which saw her as innocent Janet being corrupted by sweet transvestite Dr Frank-N-Furter (Tim Curry). The film became a global cult classic, inspiring theatrical renditions in which audiences dressed up and threw rice on to the stage.

"I did Rocky Horror because I was terrified to sing and everyone said to me: 'Why don't you sing?' At first it seemed like that movie didn't lead anywhere. I mean, that movie disappeared for years and years and then resurfaced. But it was an interesting experience and it took me on to the next thing.

"In this business, you don't have any control over the final product so you learn very early on that you do the jobs for the process. When it's finished, you can't for one minute believe it will resemble what you hoped it would be. Occasionally it turns out better."

No one is more surprised by the success of Rocky Horror than Sarandon. "People are constantly stopping me on the street to say: 'I was confused about my sexuality until that movie'." Then what do you say? "'OK. I want to thank you for that.' I'm just happy to get them through it!"

Sarandon is as compelling in person as she is mesmerising on screen. Her demeanour is invitingly low-key, without a hint of façade. Despite the fact that we are here to discuss her role in Alfie, there's no avoiding election fever. Sarandon feels it's going to be close again, but is very hopeful that Kerry will pull through.

"I hope it's going to be fair this time," she says. "I think it's going to have the largest turnout of voters since the Sixties. I don't think they can even deal with the amount of people who are registering to vote now. I just hope they all go to the polls, which is a completely different thing. I think it has to change or we will really be in trouble."

Sarandon is one of the few actors who welcomes fame, and uses it with precision. "I don't mind being a celebrity," she says, snuggling into her black pashmina to fight off the freezing air-conditioning. "All those people complain about it, but it doesn't bother me at all, because I feel I'm using it and it's not using me. I try to gravitate towards those small groups who need visibility, like the other day when I was doing press for television; I wore these dog-tags which read: 'OperationTruth'. They represent the soldiers coming back from Iraq, who are educating the public about what's really happening over there. No one's counting the number of suicides in the death toll, and the fact that there's no support when they return from the war with no healthcare."

For a second, I fear Sarandon will spend the rest of our interview sermonising about the war or her numerous other political causes, but I couldn't be more wrong. "I am choosing my words more carefully now," she practically whispers as if a little voice inside her head has instructed her to stop. "It's so easy to be labelled anti-American."

But it doesn't take much nudging to prompt her thoughts on Tony Blair. "I do not understand this Blair and Bush thing," she announces, turning up the volume. "Clinton I got, but Blair I do not get. Now he's even having a heart operation like Clinton."

She shakes her head. "Last time I was in London, I asked someone to explain him to me, and they told me that you have to align yourself with power. But what about a power that's corrupt? Then why didn't everybody align themselves with Hitler!"

One of Sarandon's redeeming qualities is her ability to attract fans of both genders. She's a feminist who also identifies with the male sensibility. Her sexuality is palpable on and off screen, and what's more comforting is that she does not appear to allow age to define her.

"Real sexuality and sensuality does become more and more interesting as you grow older," she says emphatically.

"I remember as a kid watching black-and-white movies of those sexy, Italian actresses and they were so far from the stereotypical Barbarellas which were hip at the time. There was something about them that said yes to life. They seemed so courageous and open. When I look at the sensuality of the posturing, and girls revealing their midriff now in those music videos, they don't actually seem sexy. It's as if they are all learning these moves to be sexy in the same way."

The eldest of nine brothers and sisters, Sarandon (née Tomalin) was born in New York City and grew up in New Jersey in a Catholic family. Her political consciousness developed at an early age: she was arrested for her involvement in the civil rights movement and protests against the Vietnam war while still in school.

In the early Eighties, Sarandon played girlish women who yearned for a better life, from the prostitute mother in Pretty Baby, to the card dealer in Atlantic City who washes herself with lemons, which earnt her the first Oscar nod. When Sarandon hit 40, her peers were facing ever-diminishing careers while she was just hitting her stride: an unforgettable role in Bull Durham (1988), an Oscar-nominated performance in Thelma and Louise (1991), followed by two additional Oscar nods in the underappreciated Lorenzo's Oil (1992) and The Client (1994). Other films include The Banger Sisters in which life imitated art when her real-life daughter played her daughter on screen, and the critically acclaimed Igby Goes Down.

In her latest film, Sarandon's exudes sexuality as the affluent older woman, Liz, who teaches Alfie a few tricks. Jude Law plays the debonair, swinging playboy, but underneath the bravado is a troubled man who won't get emotionally involved. This time the film is set in New York, and Alfie bed-hops from one chick to another, but is forced to face the music as his freewheeling lifestyle unravels.

Sarandon explains the attraction of the role. "I really wasn't interested in being like Shelley Winters [in the original] or playing some cheap, desperate woman. I'm a female Alfie and better at it, because I don't need to lie. I'm upfront about who I am, which is more attractive as she sees him for who he truly is, because she knows he's bluffing.

"There's still a double standard in today's world. Men are called players, and women are still called whores. When women are ambitious they are called bitches, but when you're a guy, you're just ambitious."

Would she succumb to the charms of a real-life Alfie? A smile sweeps across her face: "If they are as charming as Jude Law, I think they will be worth a dance!"

To Sarandon, love has no age limits. "It doesn't matter to me on or off screen. You can meet a 22-year-old who is very much older and more interesting than a man twice his age. I've made a lot of movies where there have been age gaps one way or another. In my own life, I've been with men who were younger and I've been with men who were much older, but in the end, I think age kind of disappears."

Pointing to her heart, she adds: "It's the fire in there what counts."